Nowadays, with the progress of production and manufacturing technologies, a large number of small unmanned aerocrafts have been applied in various fields, for example, applied in aerial photography, exploration and by flight enthusiasts. These unmanned aerocrafts include single-rotor, multi-rotor and four-axis aerocrafts. Majority of these aerocrafts are manipulated by untrained non-professional users. During the manipulation of flying, it is very likely to cause a case where rotors stop rotating. However, due to the limited flight height of these aerocrafts and different manipulation abilities of the users, especially for new beginners, the aerocrafts often fall down to the ground rapidly during test flights. In order to prevent the damage to the rotors from this sharp falling, aerocraft manufacturers often additionally provide corresponding blade guards around the rotors, so that the rotors may be protected by the guards when the aerocrafts fall down to the ground. The existing blade guard is generally mounted in two ways: first, the guard is connected to an aerocraft body by screws; and second, the guard is in snap connection to an aerocraft body. In the first way, apparently, corresponding tools are required to assemble or disassemble, and both the assembly and the disassembly are inconvenient; while in the second way, although the assembly is simple, the disassembly cannot be realized, and accordingly, the large space usage is not convenient for transportation and packaging. In view of this, some improvements are made thereto by the inventor(s).